This invention relates to a seed germination medium for encouraging the germination and establishment of seeds, especially in hostile environments, where water, nutrients, climate, chemical contamination and soil conditions may be limiting factors.
Desertification, salination and soil erosion are significant and increasing problems in many parts of the world. They are typically caused by climatic change, rapidly increasing population, shortage of water and loss of agricultural land to development. This process often places unprecedented pressure for increased productivity from a diminishing and non-renewable land resource. This often leads to contamination of the soil with salts (from contaminated irrigation water, ground water, and fertiliser use) which eventually makes it impossible to grow food or even cover crops. This in turn accelerates soil degradation and leads to desertification.
One of the few ways to reverse salination is to irrigate contaminated soils with clean water to wash-out the saline contaminants. This is often not possible due to the lack of pure water. An alternative is to establish salt tolerant species (e.g. pistachio, barley and sugar beet), then to minimise water use, and subsequently to xe2x80x98soak-upxe2x80x99 salts in the harvested crops. This is a gradual process which will allow a wider range of less tolerant crops to be grown in the longer term.
Various proposals have been made for providing seed germination media which provide the seeds with water, nutrients and protection during the germination phase.
U.S. Pat. No. 5,189,833 discloses an arrangement in which lawn grass seeds are germinated in a thin layer of growing medium sprayed over a mat of non-woven polypropylene lying on top of an impermeable membrane. After a few days of germination, the mat carrying the seed-bearing medium can be lifted, rolled and then spread over an appropriately conditioned and prepared lawn bed. It will be appreciated that such an arrangement is neither intended nor suitable for growing crops in adverse environmental conditions.
Australian Patent Application AU-A-81394/75 discloses a seed bearing mat comprising upper and lower layers bonded together with a latex adhesive, seeds being bonded between the layers. The lower layer is a water permeable material such as straw, coconut fibres, peat moss or wood shavings whilst the upper or covering layer is formed from materials of a finer texture than the lower layer such as coconut fibre dust or sawdust bonded together by latex. The seed bearing mat of AU-A-81394/75 is described as being particularly useful in preparing lawns.
French Patent Application FR-A-2505607 discloses a non-laminar seed germination medium comprising a folded layer of a transparent plastics material such as polyethylene having bonded to the edges of the underside thereof a water-soluble or degradable seed-bearing medium such as paper. In use, the seeds germinate beneath the transparent plastics layer and, as the seedlings grow, they lift the transparent layer away from the water-soluble/degradable medium. Thus the transparent layer is gradually unfolded and carried upwards by the growing seedlings and therefore remains in place over the top of the plants to maintain a greenhouse effect.
French Patent Application FR-A-2440438 discloses a peat-based seed bearing medium comprising a lower layer formed of a water-permeable fibrous material such as cellulose fibres or muslin cloth, an intermediate layer of peat containing seeds and any additives; and optionally an upper layer which is also water-permeable and can be formed from a material such as muslin. Although FR-A-2440438 discloses that the media are envisaged as being economical for large scale use such as plantations in and regions e.g deserts, it is also emphasised that an advantage of the peaty medium, compared with polyethylene sheets, is that it allows the penetration of rain water.
International Patent Application WO-A-96/28010 discloses a seed germination medium in sheet form having upper and lower layers and seeds disposed therebetween. The upper and lower layers are preferably formed from a biodegradable paper material. In order to assist anchoring of the medium in the underlying soil or, in the case of desert areas, sand, the medium is slit longitudinally to enable it to be stretched laterally to form an open lattice. However, it has been found that a problem with the lattice arrangement disclosed in WO-A-96/28010 is that it has a tendency to dry out too quickly. In particular, when stretched to open out the lattice, the edges of the lattice openings lift exposing the lower layer of the medium and increasing water loss. Also, the lifting of the edges of the lattice results in the seeds being lifted away from the soil which acts to inhibit germination of the seedlings, possibly through build up of ethylene in the medium.
It is an object of the present invention to provide a seed germination medium which avoids the problems inherent in many known media and which enables seeds to be germinated effectively in a range of different types of environment, particularly arid and semi-arid areas and areas in which soil salination and desertification has taken hold. A further object of the invention is to provide a means of assisting germination and development of seedlings in land contaminated with organic and inorganic materials such as solvents and heavy metals.
Accordingly, in a first aspect, the invention provides a seed-germination medium comprising an upper layer formed from a tissue paper having a weight of about 10 to 30 g/m2, the tissue paper being coated or impregnated with a waterproofing agent such that the tissue paper is permeable to gases but substantially impermeable to water in liquid form; a lower layer formed from a water-absorbent biodegradable material; seeds being disposed beneath the upper layer, and the upper layer optionally having a plurality of perforations therein to assist disruption of the upper layer to enable seedlings germinating from the seeds to grow therethrough.
Although the term xe2x80x9cseed germination mediumxe2x80x9d is used above and in the claims appended hereto, the terms xe2x80x9cseed matrixxe2x80x9d and xe2x80x9cseed matxe2x80x9d are also used in the specification, and such terms are intended to be synonymous with xe2x80x9cseed germination mediumxe2x80x9d unless the context indicates otherwise.
The seed germination media of the invention are of a laminar construction, and typically comprise layers bonded together in such a manner that the layers cannot readily be separated without destroying them. In this respect, the media are distinguished from the media disclosed in FR-A-2505607 which are of a non-laminar arrangement in which the upper and lower sheets are connected only at their respective edges such that the upper sheet can be lifted away from the lower sheet by the action of the growing plant.
The upper layer optionally has a plurality of perforations therethrough through which seedlings may grow. Such perforations are preferred when the seedlings are of a more delicate or less robust nature and/or are insufficiently strong to force their way through the upper layer. However, where the seedlings are of a more robust nature, and are sufficiently strong to burst through the upper layer, the perforations may be omitted.
The lower layer can also be provided with a plurality of perforations to enable roots emerging from the seeds to grow therethrough.
The coated or impregnated tissue paper from which the upper layer is formed should be partially permeable to water vapour but should nevertheless provide some barrier properties with respect to water vapour. A major function of the upper layer is to minimise loss of water from the medium through evaporation, and to hold seeds in position when exposed to wind, rain or harsh irrigation.
The term xe2x80x9ctissue paperxe2x80x9d paper as used herein refers to a lightweight material with relatively poor mechanical strength typically having a weight of approximately 10 to 30 g/m2, more usually 15 to 25 g/m2, for example from 17 g/m2 to 24 g/m2. The tissue paper typically has sufficient mechanical strength to enable it to remain intact during manufacture and laying but is preferably sufficiently weak when wet to allow stronger seedlings to grow through. For stronger grades of tissue paper, for example papers at the upper ends of the weight ranges set out above, perforations may be present in the upper layer to assist the growth of seedlings, particularly where the seedlings are of insufficient strength to burst or xe2x80x9cpunchxe2x80x9d though the tissue.
The tissue paper can be calendered to give a polished surface and an example of such a calendered paper is sulphite paper available from Kruger Tissue, Church Stretton, Shropshire, UK.
In order to provide the necessary waterproofing properties, the tissue paper can be coated with a waterproofing material such as a wax or gas permeable polymeric coatings In general, the coating of waterproofing agent is relatively thin, for example less than about 10 microns thick. The thin layer of waterproofing material is chosen so as to give waterproofing properties for a short period of time until the seedling establishes itself, but contributes relatively little if at all to the strength of the tissue. Examples of waterproofing polymers include bioerodible polymers and/or polymers which hydrolyse of otherwise break down slowly in the presence of water, air, ultraviolet light or heat, or under the action of microbial attack In an alternative embodiment, the tissue paper can be impregnated with a waterproofing material, for example a waterproofing adhesive (such as xe2x80x9cMystolene PSxe2x80x9d available from Catomance PLC, UK) which can consist of or contain a waterproofing polymer as hereinbefore defined.
The upper and lower layers are typically bonded together by means of an adhesive. The adhesive is typically one which is non-phytotoxic, and most preferably is water-based. Examples of such adhesives are starch, starch derivatives, polyvinyl alcohol (PVA) and ethylene vinyl acetate (EVA), optionally in combination with other adhesives. The adhesive can be applied in such a manner and in such an amount that it permeates the upper layer thereby providing waterproofing properties to the upper layer. Where the adhesive itself in of insufficient waterproofing capability, a waterproofing agent can be added to the adhesive. The adhesive is preferably one which is biodegradable or bioerodible.
The lower layer is an absorbent layer which can be made from a wide range of biodegradable materials including air-laid paper e.g. an air-laid latex bonded paper, for example a paper formed from fluff pulp and a latex binder; waste or recycled paper, or other fibre-based or waste products. The selection of a suitable absorbent material for the lower layer will be dependent on cost, availability of raw materials and water for irrigation; the soil type, irrigation method, degree of capillarity required and the amount of water which must be retained in the medium to facilitate establishment of the seedling. In one preferred embodiment, 38-150 gm/m2 air-laid paper is used to form the lower layer, one such form of material being available from Walkisoft of Steinfurt, Germany. Such air-laid papers typically contain approximately 85% fluff pulp and 15% latex binder, although greater or lesser amounts of binder can be used as desired. Where availability of water is not a limiting factor, the lower layer may be relatively non-absorbent, e.g. may be formed from newsprint or other recycled material.
The lower layer can be a single layer or it can comprise a plurality, e.g. two, three or four, of layers. As with the upper layer, the lower layer can be perforated to assist the penetration of roots emerging from the seeds, although with plants exhibiting strong root growth, this may be unnecessary. The upper and/or lower layer can advantageously be coloured or treated to manipulate climatic conditions (e.g. to absorb or reflect heat) and to suppress weed growth below the medium. For example, the medium, or at least the surfaces thereof, can be provided in a variety of colours to assist soil warning/cooling or to exclude light so as to suppress weed growth and aid plant establishment. The medium may have different colours on its upper and lower surfaces to enhance or reduce the absorption of radiation on one surface and produce the opposite effect on its other surface.
In order to maximise weed suppression, the perforations in the upper and lower layers are preferably not in register, thereby ensuring that the medium cannot be expanded to form a lattice in the manner disclosed in WO-A-96/28010, and hence preventing weeds growing through. The perforations can be slits or holes of any shape but, in the upper layer, preferably they are in the form of slits. The upper and lower layers can have different numbers of perforations, and the perforations in the respective layers can be of the same general shape or a different shape. In general, the placement and size of the perforations and cuts will be dependent upon seed size, shape and type.
In addition to the seeds, a range of optional materials can be disposed beneath the upper layer.
For example, fertilizers, micro-nutrients (such as zinc, copper, boron, and seaweed extracts), vitamins, humic acid, sea kelp, sugars, amino acids, plant growth promoters and hormones, pH-regulators such as lime and sulphur, salt binding agents such as gypsum (calcium sulphate) and adsorbents such as activated carbon can be incorporated into the medium either by formulating with the adhesive or by application directly to one or other of the internal surfaces as a spray, granule or dust. The pH-controlling agents can be used to control the acidity of the immediate environment, and agents such as gypsum and activated charcoal can minimise the impact of adverse chemical contaminants and salt in the soil or medium, as well as to improve germination, and/or to aid and accelerate plant establishment. Salt binding compounds, buffering and pH regulating compounds and adsorbents typically are applied at between about 20 gsm and 200 gsm, more usually 50 to 150 gsm, for example approximately 100 gsm. In the case of the adsorbent, activated carbon, lower concentrations are typically used.
The buffering and other chemical organic agents provide a means of counteracting the impact of adverse chemical contaminants in the soil or medium, as well as improving germination, and/or aiding and accelerating plant establishment. Thus, for example, lime provides a buffer against low pH, gypsum provides a means of counteracting high salinity, whereas clay minerals such as zeolite, kaolinite, calcium bentonite and montmorillonite counteract high levels of fertiliser or chemical contamination in the soil.
Fertiliser and micronutrients may be added to the medium either by incorporation with the adhesive or applied directly to one or other of the internal surfaces as a spray, granule or dust. If applied at high levels, fertilisers will produce a high level of EC (electro-conductivity) in the medium, which will scorch and kill emerging seedlings. Consequently the rate of application, the type of fertiliser used and the rate of release generally require careful control. Typically, organic based fertilisers are used since such fertilisers release nitrogen more slowly allowing higher rates to be included in the medium without risk of damage to seedlings. A typical application would be of a granular, organic-based material at between 10 and 100 grammes per square meter (gsm), more typically 30-80 gsm. Fertilisers can vary considerably in their potassium, phosphorus and nitrogen contents, but one fertiliser useful in the media of the invention contains 16% nitrogen, 10% phosphorous and 10% potassium plus micro-nutrients.
Water retaining substances and wetting agents, which can be synthetic or natural materials (such as clay minerals, e.g sodium bentonite (which can be applied at up to 100 gsm), or gelatine products, or surf such as non-ionic, anionic, cationic and amphoteric surfactants or other wetting adjuvants), can be included to increase the water absorbency of the medium. Examples of such water-retaining substances include polymeric gels such as polyoxyethylene gels (PEO), silica gels and so-called xe2x80x9csuper absorbentsxe2x80x9d such as super absorbent acrylic polymers (e.g. polyacrylamide), which may be added to the medium at between 5 and 100 gsm, preferably 10 to 40 gsm, for example up to about 30 gsm depending on use. Polyacrylamide is available for agricultural use from a range of suppliers including, for example, Glowcroft Ltd. Polyoxyethylene gels, which are particularly preferred in very hostile environments such as highly saline soils, can be obtained from SmartTech Limited of Glasgow, UK, a particular PEO gel being cross-linked polyethylene oxide co-polyurethane hydrogel
In the case of wetting agents, these assist in dispersing the water throughout the medium, and allow less absorbent forms of paper or other substrate to be used.
Thus, an advantage of the seed germination media of the invention is that they improve water utilisation. As such, they can be used to reduce the water requirement in situations (such as rice growing) where relatively large amounts of water may normally be required either to enable germination to take place or to suppress weed growth. Furthermore, not only can the seed germination media of the invention advantageously be used to enable growth to take place in hostile terrains, but they can also be used in more temperate conditions, for example in agriculture and horticulture, for example in growing sweetcorn, soya and salad crops.
Pesticides, (e.g. herbicides, fungicides, insecticides and nematicides etc.) can be incorporated beneath the upper layer and preferably between the layers. Although pesticide/micro-nutrient treated seed can be used, the pesticides can alternatively or additionally be incorporated into, or adsorbed or absorbed onto, the medium. This may reduce the concentration of pesticide (and fertilizer) in direct contact with the seed allowing a broader range of products to be used at higher rates without causing phytotoxicity, reducing the requirement for field applications and dose of active ingredient.
The seeds and optionally seeding agents such as propagation agents of plant, animal and fungal origin can be bonded or held by physical pressure at a predetermined density between the layers of the medium. The density of seeding will typically depend upon the required plant population and environmental or field factors, for example. The seeds can advantageously be treated with pesticides of the type referred to hereinabove.
Where the lower layer is formed from a plurality of sheets, each separate layer can be impregnated with or carry a different additive. Thus, for example, an upper sheet can carry the seeds whilst plant nutrients can be carried by an underlying sheet.
Biological agents such as bacterial spores and fungal propagation agents (eg mycorrhizae) or other propagation agents may be used to encourage plant establishment in hostile environments and/or provide a means of biodegradation of the upper and lower layers. Bacteria and soil fungi can buffer seedlings against soil contaminants (eg heavy metals) and may be incorporated to attack the upper and/or lower layers to encourage breakdown and the break through of seedlings. Typical biological agents may include any one or more of the following:
(a) vesicular arbuscular mycorrhiza fungi which will form symbiotic associations with the emerging roots and soil bacteria to encourage establishment, especially in extreme conditions (eg Mycor manufacture by Plant Health Care Inc. or Symbio Limited of Great Bookham, UK);
(b) Pseudomonas spp. which are nitrogen fixing end which will encourage seed germination;
(c) Bacillus spp. To enhance seeding and encourage the development of organic matter in the soil;
(d) Streptomycetaceas spp. or Trichoderma spp. to discourage the build-up of disease in the medium;
(e) other phosphorous solubilising and nitrogen fixing bacteria; and
(f) bacteria or fungi bred or selected to lock up, solubilise or inactivate a specific range soil contaminants such as hydrocarbons, toxic substances eg cyanide and heavy metals; and
(g) other microorganisms which degrade celluloses, starch and other polysaccharides.
Mixtures of bacterial plant growth activators that can be used in the seed germination media of the invention include commercially available products such as xe2x80x9cBioPakxe2x80x9d (manufactured by Plant Health Care Inc) and xe2x80x9cOrganicaxe2x80x9d Plant Growth Activator (manufactured by Organica Ltd).
Depending upon the materials used, bonding of the upper and lower layers can create a translaminar effect, which greatly enhances the movement of water across the medium from an irrigation source. The use of a semi-permeable layer on top reduces water loss from the absorbent layer, and super absorbents between layers reducing water demand.
The media of the invention can be provided with and/or used in conjunction with irrigation tubes. For example, one or more irrigation tubes can be sandwiched between the upper and lower layers or bonded to one or both of the exterior surfaces of the media. The irrigation tubes can be used together with solar pumps, for example, or heat sensitive mechanical pumps which control the distribution of water in accordance with the requirements of the media in a given set of environmental conditions. Irrigation tubes useful in the media of the invention can include trickle irrigation tubes which can be polymeric tubes having perforations along their length, or tubes formed by folding sheets of a polymeric material such as polyethylene and tacking the edges together to form a leaky seam through which water can escape during use.
The medium of the invention can be provided with reinforcing means for increasing its physical strength. The reinforcing means can be made sufficiently robust to enable the use of the medium as a ground anchoring medium in, for example, civil engineering applications, e.g. in the reinforcement of banks. In one embodiment, the reinforcing means can take the form of a mesh or netting made from a metal or plastics material, or can take the from of a fibrous reinforcement, such as a fibrous mat.
Where reinforcing means are present, they are preferably secured to the upper surface of the medium, for example by means of adhesive bonding. By securing the reinforcing means to the upper surface, the medium is held firmly in place. Moreover, irrigation tubes can be placed between the reinforcing means and the medium, the reinforcing means holding the irrigation tubes in place for as long as is required, for example to enable long term maintenance. A particular application of such an arrangement is in the stabilization and maintenance of steep or otherwise unstable embankments such as road and rail embankments, or mining spoil or as a covering on waste disposal landfill sites.
In another aspect, the invention provides a process for stabilising an area of ground (e.g. an embankment, such as a road or rail embankment, or mining spoilage or industrial or domestic waste dump, such as a landfill site) which comprises securing to the ground a seed germination medium as hereinbefore defined.
Either reinforced or non-reinforced medium can be used to stabilise an area of ground but, in cases such as embankments (e.g. roadside embankments) where the ground may be particularly unstable, the reinforced medium may be preferable.
In a still further aspect, the invention provides a method of growing a plant comprising placing a seed germination medium according to the invention on or beneath a soil surface (for example a soil which is saline) and allowing or causing germination of seedlings from the seeds in the medium, such that the seedlings grow through the upper layer of the medium, for example by growing through perforations formed in the upper surface or by disrupting the upper surface to form a hole(s) and growing through the hole(s).
In a further aspect, the invention provides a process for making the medium as hereinbefore defined, the process comprising the steps of:
(i) providing a first web formed from a material which will constitute the lower layer;
(ii) optionally forming a plurality of perforations in the first web;
(iii) depositing seeds onto the first web;
(iv) providing a second web formed from a material which will constitute the upper layer,
(v) optionally forming a plurality of perforations in the second web, where such perforations are not already present;
(vi) optionally depositing adhesive on one or both of the first and second webs; and
(vi) bonding the first and second webs together.
Moisture from adhesives applied during manufacture may initially be absorbed into the lower layer and any super absorbents present and such absorbed water may subsequently be imbibed by the seeds leading to a degree of pre-germination. As an alternative to encouraging pre-germination in this manner, seeds may be pre-treated before manufacture to pre-imbibe moisture by any one or more of a range of techniques, including fermentation and chemical treatment. The advantage of pre-germinating the seeds is that it greatly reduces the establishment time of the plant, and reduces the moisture requirement after laying, without detriment to the seed. However, where the seeds are pre-germinated, care must be taken (e.g. by seed treatment or moisture control) to avoid fungal and/or microbial attack on the seeds or physiological deterioration.
In a still further aspect, the invention provides apparatus for manufacturing a medium as hereinbefore defined, the apparatus comprising first and second support means for holding respectively the first and second webs as hereinbefore defined; a bonding station for bonding the first and second webs together (e.g. by compressing the webs together); means for advancing the first and second webs towards the bonding station; a seed dispenser upstream of the bonding station for depositing seeds onto the first web; optionally adhesive depositing means upstream of the bonding station for applying adhesive to one or both of the webs; and optionally means for perforating one or both of the first and second web prior to or after bonding to form the medium.
The bonding station can take the form of a pair of rollers, the first and second webs being conveyed through the nip between the rollers, for example after adhesive has been applied to one or both of the webs, the rollers exerting pressure on the webs to bring about bonding therebetween. The rollers preferably are relatively soft, or at least have a resilient surface, so that the seeds are not damaged as the webs pass between the rollers. Alternatively, bonding can be achieved by applying tension to the finished roll of medium. The adhesive can be deposited on the web(s) in the form of a spray (which can be for example an electrostatic spray), or by means of a roller or brushes. Preferably adhesive is deposited on the first web prior to depositing seeds on the web so as to assist in retaining the seeds on the web as it is transported towards the bonding station. Adhesive is preferably also deposited on the second web upstream of the bonding station. When bonding is to be carried out by mechanical means rather than by adhesive, such mechanical means can be provided at the bonding station.
The formation of the perforations in each web can be effected by passing the web over or through a cutter. The cutter can take the form of a pair of rollers, one having a plurality of cutting elements and the other having a plurality of complimentary recesses for receiving the cutting elements, the web being conveyed through the nip between the rollers.
In a preferred form of the invention, cutting of the webs takes place at the bonding station, the bonding station comprising a roller or rollers having laminating/compressing regions and cutting regions.
In a still further aspect, the invention provides a cutting and bonding roller for use in the apparatus of the invention, the cutting and bonding roller having one or more (preferably a plurality) axially spaced compression roller elements interspersed with one or more cutting wheels. One or more spacer elements may optionally be disposed between adjacent compression roller elements.
In one embodiment, the cutting and bonding roller comprises a drive shaft having mounted thereon a plurality of compression rollers, one or more cutter wheels being disposed between at least one pair of adjacent compression rollers; and a plurality of spacer elements, the spacer elements being interposed between adjacent cutter wheels so as to space the cutter wheels apart. The drive shaft can have one or more slots or protrusions or other keying means which cooperate with complimentary formations on the cutter wheels and optionally the spacers so as to hold at least the cutter wheels against relative rotation with respect to the drive shaft.
The cutter wheels have a plurality of cutting edges spaced (preferably regularly) around their circumference. The cutting edges can be saw toothed or arcuate in form, for example, and can be arranged in either a continuous or discontinuous array. For example, in a discontinuous array, the cutter wheel can have a plurality of cutting edges separated by non-cutting edges of a smaller radius than the cutting edges, the cutting and non-cutting edges having substantially concentric radii. In a continuous array, the cutting edges can have, for example, a substantially sinusoidal form.
In another aspect, the invention provides an adhesive composition suitable for use in the matrices as hereinbefore defined, the adhesive comprising a water soluble or water dispersible adhesive polymer such as PVA; and one or more (preferably two or more) agents selected from pesticides (for example herbicides, fungicides, insecticides, nematicides), plant micronutrients (such as zinc, copper, boron), organic and inorganic fertilisers, plant growth regulators (e.g. seaweed extract), plant growth promoters and hormones, buffering agents and pH regulators (e.g. lime and sulphur), and salt binding agents such as gypsum (calcium sulphate).